Robert De Niro’s wildly successful Tribeca Film Festival will expand to nine days when it returns for a second year this May, organizers said yesterday.

“I have just one thing to say,” the bearded, tight-lipped movie tough guy and TriBeCa resident told a City Hall press conference.

“Come on downtown!”

De Niro and his business partner, Jane Rosenthal, who founded the festival last year to boost downtown businesses in the wake of 9/11, announced that more than 200 films would be shown in the second edition, scheduled May 3-11.

They were joined by Mayor Bloomberg and actor Kevin Spacey – whose GreeneStreet Productions will sponsor a new cash award for first-time filmmakers.

Rosenthal said the popular family street fairs that drew thousands downtown last year as part of the festival would be expanded from one to two weekends.

“This year, we’re going to do it even bigger and better,” she said.

Organizers estimated that 150,000 people attended the inaugural five-day festival, which included a comedy and rock concert at Battery Park.